In recent years, in order to enhance the fuel efficiency of a vehicle, a technique has been proposed by which, for example, when a driver depresses an accelerator pedal more than necessary, a specific increment of pedaling force is intentionally added to a base pedal reaction force (base pedaling force) of the accelerator pedal, so as to produce a suitable feel of barrier to the driver who is operating the accelerator pedal, and guide the driver to an operation region which is good in fuel efficiency. For example, a patent document 1 discloses a technique of: calculating an optimal amount of operation (optimal amount of depression) of an accelerator pedal based on a driving condition of a vehicle wherein the optimal amount achieves an optimal fuel consumption rate; and correcting the calculated optimal amount of operation depending on the form of a preceding road in which the vehicle is to run; and increasing the pedal reaction force (pedaling force) of the accelerator pedal in a stepwise manner in the neighborhood of the corrected optimal amount of operation, when the driver depresses the accelerator pedal. In patent document 1, the optimal amount of operation is corrected to a smaller value, when the preceding road in which the vehicle is to run is a downhill or curved road.